March, 1905.] Powell: Wings of Certain Beetles. 19 



Sat. sol. HgCl 2 in 35 per cent, ale 60 vols. 



Glacial acetic acid (99.5 per cent. ) ...10 " 



Platinic chloride 2 percent, sol. in aq. dest 30 " 



This can be used either warm or cold, while the material should be 

 cut into as small pieces as possible. 



Out of a number of different stains tried, I selected Ehrlich's acid 

 hematoxylin as the best all round stain for the wings and other hypo- 

 dermal tissues, though Delafield's hematoxylin gave good results and 

 iron hematoxylin worked well in some cases. 



Explanation of Plates XI-XVII, Vol. XII. 



All the figures used in this paper were outlined with a camera lucida and the de- 

 tails put in with free hand. The figures are arranged dorsal side up, and the anterior 

 surface toward the reader. 



Abbreviations used in the figures : 



b, basement membrane. s v mesothoracic spiracle. 



c, head. s 2 , metathoracic spiracle. 

 ct v old cuticle. s 3 , first abdominal spiracle. 

 ct 2 , new cuticle. .? 8 , last abdominal spiracle. 

 cl s , secondary cuticle. set, seta. 



f.b, fat body. tr, trachea. 



h, hypodermis. tr.cl, tracheal cells. 



h.sp, spur of hypodermis. tr'ol, tracheole. 



l.b, leg bud. tr'ol.w, wing tracheole. 



le f cy, leucocyte. tr.cr, tracheal center. 



l.tr, lateral tracheal trunk. iv.d, wing disc. 



ms, muscle. w. b, wing bud. 



nc, nucleus. w.l, wing lumen. 



Fig. I. Tomicus plastographus. Just starting wing disc, showing tracheae 

 partly surrounded by cells of the disc. From cross-section of larva in the middle of 

 the second stage. 



Fig. 2. T. plastographus. Not quite frontal sagittal section of wing disc, 

 showing forming tracheoles at base of disc. From larva in middle of second stage. 



Fig. 3. T. plastographus. Wing disc, showing the pronounced folding and 

 ridging of the cells. From cross section of larva just before second moult. 



Fig. 4. T. plastographus. Wing disc just beginning to evaginate. From 

 cross section of larva soon after second moult. 



Fig. 5. T. plastographus. Cross-section of wing near cephalic end, showing 

 trachea pushing through basement membrane, the cells spreading out underneath it 

 and tracheoles beginning to form. From larva just after second moult. 



Fig. 6. T. plastographus. Cross-section through middle of same wing from 

 which Fig. 5 was taken, showing forming tracheoles and the bases of the cells 

 beginning to elongate and separate. 



